1. FIELD OF THE INVENTION
This invention relates to antibacterial agents. More particularly, the invention relates to thiazolo [5,4-f]quinoline-8-carboxylic acid derivatives, which are useful as antibacterial agents; to intermediate useful in the preparation of the thiazolo-[5,4-f]-8-carboxylic acid derivatives; to processes for producing the thiazolo[5,4-f]-8-carboxylic acid derivatives; and to pharmaceutical compositions containing thiazolo[5,4-f]quinoline-8-carboxylic acid derivatives which are useful in the treatment of bacterial infections.
2. DESCRIPTION OF THE PRIOR ART
It is well known that various antibacterial agents have been developed, including nalidixic acid and 6-lower alkyl-2,3,6,9-tetrahydro-3-lower alkyl-2,9-dioxothiazolo[5,4-f]quinoline-8-carboxylic acids, but these compounds have some disadvantages. For example, although 6-ethyl-2,3,6,9-tetrahydro-3-methyl-2,9-dioxothiazolo[5,4-f]quinoline-8-ca rboxylic acid shows a noticeable antibacterial activity in vitro, it does not possess a sufficient antibacterial activity in vivo.